IT8322391A1 - ELECTROCHEMICAL CELLS WITH COMPLEX SO2 ELECTROLYTES AT LOW VAPOR PRESSURE - Google Patents

Description

DESCRIPTION

of the patent application for Industrial Invention entitled: "ELECTROCHEMICAL CELLS WITH COMPLEX SO2 LETTROLLS AT LOW STEAM PRESSURE"

SUMMARY

In non-aqueous electrochemistry having a solid active cathode, an active metal anode and a highly conductive low vapor pressure electrolyte comprising a liquid solvate complex of sulfur dioxide (SC2) and an alkaline or alkaline earth metal salt, soluble in said complex, such as those having a halide anion in an element of Group 3A, the ratio of the salt to the sulfur dioxide in said electrolyte being included in the range from 1: 1 to 1: 7.

The present invention relates to electrolytes for non-aqueous electrochemical cells, and more. particularly to electrolytes which contain sulfur dioxide (SO2).

Although sulfur dioxide is an ineffective electrolytic solvent,? nevertheless it has been widely used in non-aqueous electrochemical cells with the double function of cathodic depolarizer and electrolytic solvent thanks to its high density? of energy and high capacity? of power. Without its function as a cathode depolarizer, SO2? it has rarely been used only as an electrolytic solvent, due to the fact that in addition to the poor properties? of solvation, SO2 has several other drawbacks which generally refer to the fact that it is a gas at ambient temperature and pressure (boiling point 10 ° C). For proper use, the gaseous SO2 is converted into liquid under low temperature and / or high pressure conditions, and must be kept in this liquid state by constant pressurization. As a result, SO2-containing cells had the disadvantage of requiring expensive reinforced cell containers and volatile sulfur dioxide resistant hermetic seals. Furthermore, an additional cost arose as a result of the need? of an initial liquefaction of the SO2 and of the special handling required particularly with regard to filling the cells with the volatile liquid SO2. The safety aspects of the cells containing SO2 also represented to some extent a problem since the necessary safety vent mechanisms, while providing protection, were all the same actuated by the expulsion of noxious gaseous SO2 into the atmosphere.

In order to facilitate the removal of the electrolyte and reduce the high vapor pressure of SO2, the cells generally contained organic cosolvents, such as acetonitrile, with SO2. However, despite the presence of organic cosolvents reducing the vapor pressure, the cells nevertheless remained highly pressurized with the consequent drawbacks. Furthermore, organic cosolvents, such as the aforementioned tonitrile, generally precluded cyclicality. cells and occasionally presented a potential safety problem in themselves when the cells were abused. The electrolytic salts that were found capable of dissolving rapidly in SO2 without the need? of using organic cosolvents produced cells with ineffective action, for example or they were generally probitively expensive, for example the salts of chloroborate, such as they alleviated the problem generated by the high vapor pressure of sulfur dioxide.

A purpose of the present invention? that of realizing a non-aqueous cell having a low vapor pressure electrolyte, based on S02, and a process for the preparation of this electrolyte.

Another object of the present invention? : that of realizing this electrolyte having a conductivity? very high and therefore suitable for high power application, economical both as regards the component materials and as regards their preparation; liquid under normal conditions of temperature and pressure; chemically stable in the non-aqueous cell environment; appropriate for secondary or refillable cell applications; suitable as an electrolyte for a wide range of temperatures; and devoid of free organic materials and therefore more? safe of conventional organic electrolytes.

These and other objects, features and advantages of the present invention will be more apparent. clearly from the following description and the attached signs, in which:

Figure 1 is a comparison of the vapor pressure of a prior art SO2 electrolyte and an electrolyte according to the present invention Figure 2 is a graph of the conductivities of various electrolytes according to the present invention at different temperatures,

figure 3? a graph of the cyclic characteristics? of a cell having an electrolyte according to the present invention,

Figures 4 to 7 show discharge curves of different cells having the electrolyte according to the present invention. Figure 5 also represents a charge curve for one embodiment; and Figure 8 represents a graph of the polarization characteristics of a cell having an electrolyte according to the present invention.

Generally, the present invention comprises a high conductivity electrolyte. high vapor pressure (less than 2 atm. at room temperature and preferably less than 1 atm.) based on SO2 a process for the preparation of this electrolyte; and non-aqueous primary and secondary cells having active metal anodes, such as alkali or alkaline earth metal anodes, comprising mixtures and alloys thereof and containing such low vapor pressure electrolyte. The electrolyte according to the present invention? consisting of a tightly bound solvated complex of SO2 and a salt. alkali metal or alkaline earth metal, soluble in them, such as those in which the anion of the salt? consisting of the halide of an element of Group 3A (of the Periodic Table). The elements of the Group which are preferred for the salt are ilboron, aluminum, gallium and indium and the alkali and alkaline earth metals, preferred are lithium, sodium and calcium. Examples of Group 3Ap salts referred to for SO2 complex formation include:

and their mixtures. Non-adapted Group 3A salts complex with SO2 include II and L.

Salts that do not complex with SO2 are for? be dissolved in the solvated complex.

The solvated complexing of the SO2 and the salt depends on the equivalent ratios of the materials instead of? from the ratios of moles, this difference being evident, for example, with respect to the alkaline earth metal salts which generally contain two equivalents per mol. Equivalent ratios are included in the range from 1: 1 to 1: 4 ((salt: S02) and due to this variation the combination of the salt and the S02 has been shown to be of the nature of a complex rather than a new compound formed by reaction. Although the actual complexing of the salt into SO2 is generally up to a ratio of 1: 4 (salt: SO2), the addition of uncomplexed SO2 to the cell in an amount of up to about 1: 2 ( salt: total S02) will not pressurize the cell in a harmful way at room temperature. of the electrolyte is also reduced. Electrolytes such as 1: molar in SO2 (equivalent ratio of approximately 1: 22 as described in U.S. Patent No. 3. 493. 43 3 are highly pressurized (approximately 3.5 atm.) And as described in said patent are actually It is used at temperatures between 10 ° C and -30 ° C. Since it is not available in a complexed form with only a minimal content if there is one of non-complexed SO2, the SO in the electrolyte does not act as a cathode depolarizer. Therefore, the electrolyte of the present invention is mainly useful in electrochemical cells having solid cathode depolarizers. Such cathodes include

as well? other metal halides, oxides, chromates, vanadates, titanates, tungstates, chalcogenides and active non-metallic cathodes, such as conductive, organic polymers, such as polyacetylene, poly-p-phenylene, polyphenylene sulfide and various carbon compounds, such as

Bench? it would be presumable that the solid cathodes would make cells having a capacity? of high power compared to the cells, having fluid cathode depolarizers such as SO2, this reduction? in reality? minimized by the unexpectedly very high conductivity? of the electrolyte according to the present invention. Furthermore, the advantages of a substantially non-pressurized system, particularly in regards to the greater safety, abundantly compensates for any reduction in capacity. of high power.

The solvated complex electrolyte according to the present invention is prepared by reacting the SO2 with the alkali or alkaline-earth metal salt up to the necessary equivalent ratios. Such a reaction can? be influenced by substantial saturation of S02 liquefied with the salt up to the necessary equivalent ratios.

Do you prefer it for? that the salt is reacted with the SO2 in gaseous form, by passing a stream of dry SO2 through the salt, so that an exothermic reaction takes place with the formation of a liquid solvate complex.

The resulting liquid has a low vapor pressure of with a boiling point of 40 C) and can? be handled as a liquid in contrast to liquefied S02 (point of

boiling of 10 ° C) which must be handled in a special way as a volatile material. Figure 1 illustrates the comparison of vapor pressure

of a prior art electrode containing SO2 (curve A) and of a solvate complex of

3.5 (curve B) at various temperatures. At room temperature (20 C) the prior art electrolytes have high vapor pressures (about 3.5 kg / cm2 or about 3.5 atmospheres), while the solvated complex has a vapor pressure of about

en below the atmospheric pressure of 1.05

The solvent complex electrolyte pressure feed? logarithmic with an increase in temperature at a pressure of 4.21

There? ? in further marked contrast with the approximately 1.8.3 kg / cm2 of the electrolytes of the prior art containing SO

It should be noted that the must not

rly be reacted with the salt for himself, but he can? in reality? be reacted, for example, with Lewis acid and the basic components of the salt, so that the salt and the liquid solvate complex are proceeded simultaneously. for example, a current of dry S? 2 can? be passed through a salt of or a 1: 1 stoichiometric mixture of Lewis acid and its basic components, ^ for pr? -.

last the same liquid solvate complex as

- "x" having been determined as included in the range from 1 to 4 (equivalent bases). A c? Ntinuation of bubbling results in a value pi? high for "x" within the limits of said range Lower values for "x" can be obtained by evaporating some of the 2 from the liquid solvate complex. An addition of a quantity? excessive as described above, with which the ratio of total SO to salt? pi? 7: 1 big shape for? an undesirable pressurization of the electrolyte {over about 2 atm. ).

Conductivity at room temperature of solvated complexed electrolyte of

? how ? been discovered, about what? the maximum conductivity? observed, even in any non-aqueous electrolyte. It was found that the second electrolyte? the invention? very stable with lithium anodes and? It has also been found that it enables lithium to be electrochemically plated and stripped with efficiencies of over 97% even over extended cycling regimes, so that it? an electrolyte eminently suitable for rechargeable cells of lithium or other alkaline or alkaline earth metals.

A sol vated complex of i

while it has a slightly lower conductivity of

(but always very alavata), has the advantage of a good operability? at low temperature, for example a conductivity?

even at -30 ° C. - In contrast to solvated complexes which freeze at temperatures between about 8 C and -15 C, solvated complexes freeze at about -44 C and are more? suitable when low temperature operation is desired. A solvated complex of which has a conductivity of at room temperature and around -35 in reality? it does not freeze but becomes immobile at about -50 C. Consequently, it can? solvated complexes, such as

realizing an electrolyte having both a high conductivity and a capacitance? extremely low and high temperature.

Alternatively,? it was discovered that the incorporation of quantity? additives of inorganic solvents, such as

once the electrolyte of the solvated complex is reached, it also serves to increase the capacity? low temperature. For example, a blend of 90% (by weight) of? and 10% of (keeping it at about 25 C with a conductivity of about

Although it was found that lithium? stable in the presence, for example, of electrolytes of solvated complexes of secondary or refillable cells, it is preferred that the complexed salt contains cations corresponding to the anode metal.

For primary cell applications, other salts, such as the aforementioned sodium and calcium salts? can be used effectively with lithium anodes particularly to obtain an increased capacity? low temperature. Additionally and preferably for application in primary cells, electrolytic salts normally insoluble in SO2 alone can be used by stoichiometric complexing both with

both with organic cosolvent, such as acetonitrile; esters, such as dimethoxyethane; propylene carbonate and the like. Such salts include

The organic cosolvent yields

these salts are soluble in S02. The organic cosolvent? present only in quantity? sufficient to co-complex the salt with the absence of free organic material risks. With this co-complex also soluble salts can be used analogously.

The fact that the electrolyte according to the present invention has a low vapor pressure despite its S02 component entails several very important economic and safety advantages. Cells made with it do not need to be reinforced or otherwise made resistant to pressurized contents. The vent, if necessary such as; safety precaution, not d? resulting in the emission of noxious fumes on S02 which spread rapidly. Hermetic sealing devices for cells are not as susceptible to degradation due to the bonded state of the normally corrosive S02, and actually? can you use sealing devices pi? inexpensive suitable for non-pressurized cells. With the exception of the initial relatively simple procedure of forming the liquid solvated complex electrolyte as described above, no? no special handling or storage required in the warehouse contrary to the handling of non-complexed volatile S02. The filling from the cells with the electrolyte to the filling d? cells with a pressurized volatile liquid such as SO2.

In order to illustrate more? completely the properties? and the advantageous aspects of the electrolyte according to the present invention are described in the following Examples. It is understood, however, that such Examples are illustrative in their nature and should not be considered limiting of the present invention. Unless otherwise stated, all parts are parts by weight.

EXAMPLE 1 - Quantity stoichiometric of

were introduced into a glass container and del

dry was passed through the salt particles. A clear liquid solvate complex of

it formed? rapidly with heat generation, and after cooling to room temperature it was determined that the molar or equivalent ratio of overall solvate was 1: 3.1. The continuation of the bubbling of the

dried through the LiCl and gave another clear liquid solvate complex having an equivalent ratio of 1: 3.1. The evaporation of a small amount? from the solvate complex gave another clear liquid solvate complex having an equivalent ratio of 1: 2.6. The conductivity? of the three liquid solvated complexes, at various temperatures, were measured as illustrated in Figure 2 as curves C, D and E respectively. The conductivity? obtained were the most? never obtained for non-aqueous electrolytes. Furthermore, the lithium metal stored in the electrolyte for periods of more than four weeks showed no corrosion thus indicating stability. of such solvated complex electroites in lithium-containing cells.

EXAMPLE 2. A solvate complex was formed as in Example 1, but with NaCl instead of LiCl with its conductivity. at the various temperatures shown in

figure 2 as curve F.

EXAMPLE 3. A solvate complex of - equivalent ratio molar ratio) was formed as in Example 1, but with a stechimetric ratio of; Conductivity at different temperatures? shown in figure 2 as curve G.

EXAMPLE 4. A mixed solvate complex of

molar ratio) was obtained by passing through (molar ratio of 9: 1: 4). The resulting liquid solvate complex gave conductivity. at different temperatures, indicated "in Figure 2 as curve H.

EXAMPLE 5. A solvate complex of a mixture 90

was prepared and gave conductivity? at various temperatures as shown in Figure 2 as curve I. EXAMPLE 6. A limited cathode electrochemical cell was formed with a 2 g cathode of 60% graphite and 10% polytetrafluoroethylene (PTEF) pressed on a nickel 2 grid, 5 cm x 4.1 cm interspersed in sandwhich by two lithium anodes each of similar dimensions. The cell was filled with the electrolyte of solvated complex and discharged at the speed. of 4 up to a final voltage of 2.6 volts and charged at the speed? of 20 m up to 4.05 volts on a continuous cycling regime. The cell was made to perform about 350 cycles at a percentage close to 100% of the capacity. of an electron transfer cathode?. The charge and discharge curves for cycles No. six, No. 0.173 and No. 230 are shown in the figure. The capacity cumulative up to this point? d 72 Ahr with about 36 Li rotations (97% effective on the anoto). The capacity initial theoretical primary was 0.24 Ahr.

EXAMPLE 7. These cells were prepared as in Example 1, but with the solvated coplex electrolyte, L of Example 4. The cells were discharged at speeds. 20mA, 40mA and 60mA respectively, with the charging results shown in Figure 4.

EXAMPLE 8. A cell was prepared as in Example 6, but with the solvated complex electrolyte of Example 3 (90%). ? ric of the sixth cycle? shown in figure 5.

EXAMPLE 9. A cell like that of Example 6 was prepared, but with a 3 g cathode composed of 60% CuO, 30% graphite and 10% PTFE. The cell was discharged at 40mA with the results shown in Figure 6.

EXAMPLE 10 A cell was prepared as in Example 6, but with a cathode of 3 g consisting of 30% graphite and 10% PTFE. L? cell was discharged at 40 mA and the results are shown in Figure 7.

EXAMPLE 11. A spiral wound cell having 15.9-cm x 2.5 cm of lithium and 1? cell being cathodically limited to a capacity? theoretical of 0.75 Ahr, was filled with the electrolyte of Ex.1. an initial open circuit voltage of 4.0V. The cell was then discharged at 85 ma and erog? a capacity? 0.56 Ahr at a final voltage of 2.0 V. Was the cell charged? 40ma for 14 hours and discharged again at 40 ma delivering 0.40 Ah at the second discharge. Figure 8 shows the polarization of the cell during discharge and charge.

The effective utilization of the electrolyte according to the invention can alleviate the problem concernen

Claims (12)

1. Non-aqueous electrochemical cell having a solid active cathode and a liquid electrolyte, characterized in that the electrolyte? consisting of a liquid solvated complex, at low vapor pressure of a) sulfur dioxide and b) one or more? salts of alkali alkaline earth metals, soluble in sulfur dioxide, and that the equivalent ratio of the said one or more? do you salt the SO2 in the electrolyte? included in the from 1 to 1: 7. 2. Cell according to rev. 1, characterized by the fact that the said one or more? sal contain, halide anions of elements of Group 3A. 3. Cell according to rev. 1, characterized by the fact that one or more? salts are chosen 4. Cell according to rev. 1-3 characterized by the fact that said solid active cathode? consisting of a material chosen from the group composed of metal halides, oxides, chromates, vanadates, titanates, tungstates, chalcogeners, polyacetylene, poly-p-propylene, propylery sulphide, ? 5. Cell according to rev. 1-4, characterized in that the said active metal anode? consisting of lithium. 6. Cell according to rev. 1-5, characterized by the fact that the said equivalent ratio? included in the range from 1: 1 to 1: 4. 7. Cell according to i and rev. 1-6, characterized by the fact that the said electrolyte? further constituted by an organic electrolyte which with the said 'is co-mplexed with the said one or more? salts. 8. Cell according to rev. 1-7, characterized in that said cell further comprises an inorganic solvent selected from the group consisting of their blends. 9. Method for preparing the liquid solvate complex according to claims 1, 2 or 3, characterized by the fact of including the operations of putting in gaseous contact with said one or more? salts in solid form and to form and remove the liquid solvate complex. 10. Method for preparing the liquid solvate complex according to claims. 1, 2 or 3, characterized by the fact that it comprises the operations of contacting the Lewis acid components and bases of the said one or more? salts in solid form, to form said salt and said liquid solvate complex and to remove said liquid. 11. Non-aqueous electrochemical cell, at low liquid pressure, comprising a lithium anode, a solid active cathode and a liquid electrolyte consisting of complexed with one or more? salts chosen from the group consisting of LiAlCl4 characterized by the fact that the equivalent ratio of the said one or more? salts in the said liquid electrolyte? 1: 1 to 1: 4. 12 Low vapor pressure electrochemical cell, according to rev. 11, characterized in fact that the solid active cathode? consisting of an element chosen from